Flexible shell printing element

ABSTRACT

A character supporting type shell for use with a character-bycharacter printer is disclosed. The shell is constructed of a material and has a shape that cause it to have rotational and longitudinal rigidity when rotated and longitudinally reciprocated about and along an axis, respectively. In addition, the shell has radial resilience so that it is deformable when acted upon by a force in an appropriate direction and of an appropriate magnitude. The resultant structure is one which has a weight considerably less than prior art devices and also a reduced inertia. The last-named factors contribute characteristics which permit a greater printing rate than previously available.

1, mte tats t 1 1 Ralph [54] EILEXHELE SHELL EElNTHNE 2,044,550 6/1936 Teissedre ..197/ss ELEMENT 4 2,838,156 6/1958 Griflith ..197/53 3,175,671 3/1965 Lapointe et al. .....197/18 x (721 Invent: 3,247,941 4/1966 Beattie eta1.... ..197/1sx [73] Assignee: The Singer Company 3,353,647 11/1967 Hugel ..197/53 X 3,406,807 10/1968 Sasakietal..... ....197/53)( [221 F1164 APT-7,1969 3,447,656 6/1969 Nyquist ..197/53)( [21] Appl. No.: 814,052

[52] US. Cl ..197/54, 197/53, 197/55, 101/109 51 11m. (:1. ..1j 1/22 [58] Field ofSear-ch ..197/54, 53, 18, 55;101/376, 101/1 1 l, 109

[56] References Cited UNITED STATES PATENTS 223,337 l/1880 Gmeiner ..101/376 1,094,299 4/1914 Brown ....101/11l X 2,987,991 6/1961 Johnson et al. ....l0l/376 X 3,068,785 12/1962 Ahlburg ....101/376 X 3,164,084 l/l965 Paige .,.101/l1l X 433,820 8/1890 Quentell ..197/53 441,198 1111890 Schuckers et a1 ..l97/53 723,855 3/1903 Frantz ..197/53 1,450,627 4/1923 Darnley ..l97/54 X Primary ExaminerEdgar S, Burr Attorney-George W. Killian, Charles R. Lepchinsky, Patrick J. Schlesinger and Jay M. Cantor [5 7] ABSTRACT A character supporting type shell for use with a character-bycharacter printer is disclosed. The shell is constructed of a material and has a shape that cause it to have rotational and longitudinal rigidity when rotated and longitudinally reciprocated about and along an axis, respectively. in addition, the shell has radial resilience so that it is deformable when acted upon by a force in an appropriate direction and of an appropriate magnitude. The resultant structure is one which has a weight considerably less than prior art devices and also a reduced inertia. The last-named factors contribute characteristics which permit a greater printing rate than previously available.

3 Claims, 7 Drawing Figures PATENIEUIEB awn 31640369 SHEET 1 or 2 nvvavron Fi 4 Fi 4C DONALD L. ROLPH BACKGROUND OF THE INVENTION Character-by-character printers have been made in a wide variety of forms, most of which belong to one of two broad categories: (a) type bar printers and (b) single element printers. The invention disclosed herein relates to single element printers and, therefore, only printers of this variety will be discussed herein. One form of single element printers employs 10 what is known as a type box which is a rectangular frame supporting a plurality of individually movable type elements. To select a specific character, the type box is moved in X and Y directions until the required character is in the printing position and then the type element is driven forward relative to the box to effect printing. Such printers have been widely used for many years. Another form of single element printers employs a rigid print element which has the full alphanumeric font formed thereon. One commercial form of such a printer is sold by IBM under the trade name Selectric and uses print element which has a generally spherical shape. The Selectric print element is rotated about an axis and tilted about another axis for character selection and then pivoted towards the document to effect printing. Various other shapes of rigid print elements have been used in other printers and include cylinders and sections of spheres.

SUMMARY OF THE INVENTION The present invention employs a new and novel print element which, at first, appears to be just another version of a single cylindrical print element. The greatest point of distinction resides in the fact that the print element of the present invention is not totally rigid. The present print element may comprise a unitary structure having integrally formed characters, or the characters may be individual elements suitably affixed to the supporting cylindrical shell.

The supporting cylindrical shell is of a material which is resiliently deformable. The material, structure, and shape of the shell are such as to provide rotational and longitudinal rigidity and stability during rotational or longitudinal motion about or along, respectively, the axis of the cylindrical element. The rotational and longitudinal motions referred to are used to produce character selection. When character selection is complete, printing is effected by driving the portion of the cylinder, including the desired character, towards the document. The driving means may comprise a hammer inside the cylinder or it may comprise cylinder deforming means which causes distortion of the circular cross section of 50 cylinder so as to drive the selected character towards the document. This last may be accomplished by squeezing the cylinder at diametrically opposed points which are each 90 from the selected character.

The cylindrical print element of this invention is not its own print hammer and therefore the print element can be made lighter than any prior art print element. With a lighter print element, character selection may be faster as the lightweight print element may be accelerated and stopped faster and with less force. It should be specifically noted that the hammer element for effecting printing is not required to be moved during character selection.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a view of a typical print element incorporating the invention;

FIG. 2 is a top view of the shell and platen with dotted view which illustrates and exaggerates shell distortion during a print operation;

FIG. 3 is a cross section showing the hammer, platen, document and shell element;

FIGS. 4a, 4b and 40 show details of how an individual character may be retained by the shell; and

FIG. 5 is a partial view ofa molded print element.

2 DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 illustrates a typical embodiment of a print shell incorporating the present invention. The cylindrical shell 101 is composed of a material which exhibits rigidity when rotated about its cylindrical axis 110 and when reciprocated along the same axis and yet which is resilient when subject to a linear force at right angles to the said axis. For the purposes of this specification, the shell 101 will be said to have rotational rigidity, longitudinal rigidity, and radial resilience. More specifically, rotational rigidity is intended to convey the concept that the dimensions and geometrical form of the shell undergo relatively little change in response to the forces exerted on the shell 101 by rotation of the shell about the cylindrical axis 110 of the shell at the angular accelerations and velocity used. Longitudinal rigidity is intended to convey the concept that the dimensions and geometrical from of the shell 101 undergo relatively little change in response to the forces exerted on the shell 101 by reciprocation of the shell along the cylindrical axis 110 of the shell at the linear accelerations and velocities used. Radical resilience is intended to convey the concept that at least the geometrical fonn of at least part of the shell 10] is subject to a temporary change in response to the application of a net linear force acting along a radius of a circular cross section of the shell 1011. Note specifically that resilience means the shell 101 restores to its original shape when the distorting force is removed.

By way of explanation and emphasis, it should be un derstood that a steel cylinder having substantial thickness would satisfy the longitudinal and rotational rigidity requirements, but that it would not satisfy the radial resilience requirement. A rubber cylinder might satisfy the radial resilience requirement but not the rotational rigidity requirement. That is, a rubber shell would tend to increase in diame ter in response to rotation.

A suitable shell material is one having properties similar to those of the ubiquitous ping-pong ball. One material which has been found to have suitable qualities is sold under the trade name Delrin. The functional requirements of the concept require a material from the class that follow Hookes law. That is, a material wherein the strain is proportional to the stress within the elastic limit of the material. In addition, the material should have a modulus of elasticity low enough to provide relatively easy radial deformation. Of course, the material must be sufficiently thick for easy manufacturing and handling and to provide adequate support for the individual type elements. Materials called engineering plastics are ideally suited for the present application; such materials being characterized as those synthetic materials which obey Hookes law. It should be observed that appropriate metals are not excluded. For example, a thin steel shell having characters embossed thereon, or welded thereto, could be used. Those familiar with available materials and their characteristics will be able to select others that are applicable.

The shell 10] may assume a variety of dimensions depending upon the total number of alphanumeric characters it is to support. In general, current printers tend to standardize on character sets of 48, 64, 96 or I28 characters. The characters may be distributed about the shell surface in a variety of arrangements of ranks and columns. For example, a 48- character set could have two ranks and 24 columns; three ranks and 16 columns; or four ranks and 12 columns, as well as other possible combinations. Various factors determine the most appropriate font size and character layout for a given application. The present invention is suitable for use with a wide variety of font sizes and layouts.

Printers are required to print at as fast a rate as possible when controlled by some sort of automatic means such as a tape or card reader. Fast printing means rapid character selection. Rapid character selection may be facilitated when a small character set is used. For this discussion, it will be assumed that the size of the character set is fixed. Other factors which facilitate rapid character selection in printers of the general type under consideration include the weight of the material that must be moved and the distance it must be moved. Obviously, a low weight and small distance are advantageous. Another significant factor is the inertia of the body to be moved. For the most part, the size of the printed character sets the minimum distance that the print element must be moved for character selection. Thus, the major areas in which design advantage can be achieved are in reducing weight and inertia. The print element disclosed herein is believed to reduce the weight to a nearly irreduceable minimum. Tests indicate that the weight of a print element constructed in accordance with the teachings of this invention will have a weight of approximately one-third that of the nearest weight competitor having a similar type set. The inertia advantage, although significant, is not quite as great, as the weight of the print element constructed in accordance with the teachings of this invention is concentrated at a maximum distance from the center thereof.

A print element such as that shown in FIG 1 and which has 16 characters per rank may have a diameter of approximately one inch; the shell thickness would be of the order of 0.01 inch. The characters may be molded into the shell or individual characters may be adhesively attached to the shell 101, However, it is anticipated that individually replaceable characters which are inserted into individual openings in the shell will find greater favor in the industry as it permits the use of any desired coding and the use of specialized characters without the redesign of the whole print element. In addition, individually replaceable characters permit the economical replacement of a worn or damaged character without the need to replace the entire print element and character set.

As will be seen from FIGS. 2 and 3, the shell 101 supporting the type characters thereon will be elevated and rotated so that the desired character is brought opposite the printing point along the platen 201 which supports the document 202 which receives the printed character. A hammer 312 inside the shell 101 will displace the selected character toward the platen 201 and cause printing to take place. The shell.101 will distort from its circular cross section to an ovoid. The radial resilience of the shell 101 will cause it to return to its circular cross section when the print hammer 312 restores to its normal position. A significant advantage is obtained in the present structure over that of a typical type box in that in the present structure the individual type elements do not slide back and forth and thereby produce wear with the attendant eventual loose fit. A further advantage is obtained in that no oiling is required as with a type box arrangement. A further advantage of the present structure resides in the reduced mass that is moved to effect a printing operation. This permits a more rapid print stroke with a corresponding increase in characters printed per unit time and also a minimized tendency to smear. All of these improvements are made possible by the use ofthe nonrigid shell 101.

As may be seen from FIG. 1 and FIG. 1 taken together with FIG. 3 the shell 101 is retained on the yoke 301 by means ofa plurality of retaining members 102. The retaining member 102 may have a triangular cross section as seen in FIG. 3 and mate with a correspondingly shaped recessed portion of yoke 301. In order to fit the shell in place over the yoke 301 two slots 111 are provided for each retaining member 102. The retaining member may be molded into the shell or adhesively attached as may suit the manufacturing techniques used. In order to guarantee that the print element is properly oriented it must be keyed to the shaft. This may be done by so locating the plurality of retaining members 102 that the print element fits onto the yoke 301 in only one position. However, it is believed that the use of a keyway opening 112 in the shell 101 and a mating protuberance on the yoke 301 will meet with greater user appeal. If expedient, an additional belt or retaining clip (not shown) could be placed in position around the circumference of the shell 101 in the area of the retaining member 102 and the keyway opening 112. Other convenient means for attaching the print clement shell 101 to the yoke 301 will occur to those skilled in related arts. There may be a reduced possibility for the shell 101 to assume an oval shape in the first rank above retaining member 102. If the shell cannot be deformed as required in the lower ranks, poor print quality may result. To minimize possible derrogation of print quality, the vertical distance between the clamping area 102 and the rank 103 should be kept as large as possible. In addition, the shell 101 may be perforated as shown at 104, above the retaining member 102, to facilitate shell distortion for rank 103. By this means, it is possible to obtain substantially the same shell distortion and print quality in response to a hammer action at ranks 103 or 105 and any intermediate rank. To obtain greater uniformity of shell deformation a rib in the area of the upper ranks may be used to provide greater equalizing stiffness.

The geometry of the perforations used at 104 on the shell 101 was found to exert a marked influence on the obtaining of uniform print quality. The pattern illustrated in FIG. 1 was found to be eminently satisfactory for use with a print element comprising 4 ranks and 16 columns. The perforations were repetitive being duplicated a total of four times around the circumference of the shell 10]. That is, the illustrated pattern of perforations 104 have a cycle width of4 of the shell columns. Print elements constructed with a different number of ranks and columns might employ a difierent perforation pattern 104.

Referring now more specifically to FIG. 2 there is shown therein a top view of the shell 101 on axis and its relationship with a platen 201 which supports a document 202. The distance between the platen 201 and the shell 101 is shown greatly enlarged for convenience in illustrating the principles involved. In an actual application, the distance between the platen 201 and the printing face of a character element (only one of which is individually shown in FIG. 2) is of the order of 0.050 inches. As already explained, the shell 101 is constructed ofa material which is radially resilient. Accordingly, after the shell 101 has been rotated about its axis 110 to the desired column; and after the shell 101 has been moved longitudinally along its axis 110 so that the desired rank is in position, a force may be applied in the direction of the arrow 203 to drive the selected character towards the document 202 and effect a printing operation. It should be understood that a conventional ribbon is disposed between the shell 101 and the document 202. The ribbon is not shown herein in any view as it does not form an integral part of the invention and its inclusion in the drawings would serve no useful purpose and only tend to obscure the actual invention.

The force applied in the direction of the arrow 203 will tend to distort the shell 10] so that it will take an oval shape such as 101. It should be understood that the distances and shapes are exaggerated in FIG. 2. The force may be applied by any typical hammer means and would normally constitute a quick blow with a minimum dwell. That is, the hammer would be returned to its home position as rapidly as practical. In general a fast hammer action provide a cleaner document appearance with minimum blurring and permits a faster printing rate.

The radial resilience of the shell 101 will cause it to return to its normal round cross section as soon as the distorting effect of the hammer is removed. An alternate technique for generating a printing action is to provide equal and opposite forces 204 and 205 which will also tend to distort the shell 101 to shape 101 and drive the selected type character towards the document 202 and cause a print action. Referring now to FIG. 3 there is seen a side view of the shell 101 and an end view of the platen 201 There is also shown the rudiments of a mechanism for character selection and the print impression means which will be described hereinbelow.

The shell 101 is releasably attached to a yoke 301 which has a center bore 302. The shell 101 is retained on the yoke 30] by retaining member 102 so that the yoke 301 and shell 101 will move as a unit. This is, angular rotation of the yoke 301 results in a corresponding angular rotation of the shell 101; and a longitudinal reciprocation of the yoke 301 results in a corresponding longitudinal motion of the shell 101. The yoke 301 includes as an integral part thereof an annular rack 303 which meshes with spur gear 304. Spur gear 304 may be selectively rotated by means (not illustrated) to effect the raising and lowering of the yoke 301 and shell 101 in order to position the desired rank of characters at the desired position relative to the platen 201 to permit printing. Rotation of the yoke 301, and a corresponding rotation of the shell 101 is accomplished by the rotation of gear 305 which meshed with gear 306 formed on the lower portion of yoke 301. Gear 305 may be turned by any suitable means, as for example a stepping motor represented by box 307.

The yoke 301 is slideably supported on cylindrical frame member 310. Frame member 310 includes an arm 311 which supports bell crank hammer 312 at pivot 313. The hammer 312 is normally biased in a clockwise direction (as viewed in FIG. 3) by spring 314 which is attached to frame member 310 and hammer 312. Extending through the center of frame member 310 is a hammer actuator 315 which coacts with end 316 of bellcrank hammer 312 to pivot said hammer 312 counterclockwise about pivot 313 against the force of spring 314. The hammer actuator 315 is selectively and timely reciprocated by any convenient and conventional means actuating mechanism represented by box 330.

The hammer 312 of FlG. 3 is shown in flight between its rest and print positions. If it is assumed that the hammer 312 is moving counterclockwise, that is towards the printing position, the hammer 312 has just engaged the back of type element 320. Hammer 312 will continue to rotate counterclockwise and drive said element 320 forward towards the platen 201 and simultaneously cause a deformation of the shell 101 so that the shell assumes an oval cross section instead of a circular cross section. The radial resilience of the shell material 101 permits the said distortion.

At the conclusion of the print stroke the hammer actuator 315 moves down and the harruner 312 is pivoted clockwise by the action of the spring 314. Because of the resilient property of the shell 101 it resumes its original circular cross section thereby returning the type element 320 to its normal position away from the platen. As already indicated the type element 320 moves about 0.050 inches towards the platen 201 to engage the document and print a character. FIG. 3 does not illustrate a print ribbon which would normally be positioned between the document 202 and the type element 320. The document 202 is held in contact with the platen 201 by conventional means including a paper bail roller 340. As has been indicated, the shell 101 may be a thin wall support for individual type elements which are inserted into individual receiving perforations of the shell 101. This structure permits the simple removal and replacement of type elements when and is expedient.

FIGS. 4a, 4b and 4c illustrate a means that might be used to make the shell 101 support an individual type element 320. The shell 101 has a hole therethrough as shown in FIG. 40. The hole, while generally rectangular, would be somewhat in the form of a very fat I in that there are little seriflike additions 402 at each comer. The seriflike additions 402 permit the flexure of the shell 101 along the edge 401 to permit insertion and removal of an individual type element 320 in a manner to minimize any tendency of the shell 101 to crack or split at the corners 402 of the openings. In addition the seriflike additions 402 to the rectangular hole help the edges of the shell to support the type elements 320 in a uniform manner from rank to rank and thereby improves the quality of character impression. FIG. 4a shows a side view of a type element 320 inserted into the shell 101. The element includes a type character 421 which is curved in this view to match the curvature of the platen 201. The type element 320 includes bevels 422 to facilitate insertion of the element 320 into the hole in the shell 101. Although not necessary, the individual type element 320 may include a shoulder 427 which engages the front surface of the shell 101 when the elemented 320 is properly inserted. FIG. 4b is a top view of the same element 320 shown in FIG. 4a and as may be seen in FIG. 4b shoulders 423 are included to engage the front surface of the shell 101 along edges 401. In a similar manner rear shoulders 424 are included to engage the rear surface of the shell 101 along edges 401. In order to hole the type element 320 accurately aligned on the shell 101 so that there can be no relative motion therebetween the slots 425 formed on the element 320 must have an accurately controlled depth and backwall 426 so that said backwall 426 contacts the edges 401 of shell 101 when the element 320 is inserted.

A printer incorporating a type shell of the nature disclosed herein could be used in an operator oriented machine or in a printer which responds to input signals which may emanate from a computer, a tape or card reader or other source. The printer may be of either the moving or stationary platen type. In general, the stationary platen type is more convenient for use in applications wherein it is desired to print on continuous forms.

Depending upon engineering design, the specific application of the printer, and other considerations, the character selecting mechanism may or may not include a retum to home" feature. In a like manner a last character visibility feature may or may not be employed. In general a last character visibility feature is considered unnecessary unless the printer is an operator oriented machine.

It is anticipated that the shell 101 with individually replaceable type elements 320 will be more popular than a molded element. However, if desired a molded element may be made. Because it is not practical to mold members with extensive thin wall sections, the molded form of the shell 101 together with the print impression character might look somewhat as shown in FIG. 5, which is a top view. The shell would be quite thin in the areas 501 between characters. This would provide the necessary radial resilience. The character forming part of the plastic shell 101 could be given a metallized plating in accordance with techniques already used in analogous arts.

A printer constructed in accordance with the principles disclosed herein has several advantages over prior art printers. The advantages include:

a. a pring element of small size, light weight and having no moving parts,

b. possible customizing of type font through replacement of individual type impression characters,

c. the use of standard type impression characters of hard material and having long life,

d. the application of a constant force for the printing of each character,

e. a high rigidity-to-mass factor in the character selection mode, and low print energy loss in a printing action, and

f. a minimized tendency to print portions of adjacent characters because the effective radius of the shell is reduced by the shell deformation in the area of the character being printed.

While there has been shown and described what is considered at present to be the preferred embodiment of the invention together with some obvious variations, modifications of the invention will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the embodiments shown and described, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A multicharacter print element for a character-bycharacter printer comprising:

a. a freestanding shell comprised of rigid material and having a cylindrical shape and inherent rotational and 1ongitudinal rigidity and having substantially stable shell dimensions irrespective of the application of rotational and longitudinal forces;

b. said freestanding shell also having radial resilience for permitting at least limited temporary deformation of said freestanding shell without compression or expansion of the rigid material thereofin response to a net linear radial force on said freestanding shell;

. a plurality of type impression characters disposed on the surface of said freestanding shell for providing a print impression in response to a net linear radial force on said freestanding shell to effect said limited temporary deformation;

. means for selectively subjecting said freestanding shell to An alphanumeric print element comprising:

a plurality of individual type impression characters;

. a freestanding shell comprised or rigid material having rotational and longitudinal rigidity;

. said freestanding shell and type impression characters assembled in cooperative relationship for maintaining each of said type impression characters in an individual fixed location on said freestanding shell;

. said freestanding shell having a cylindrical shape; means for selectively moving said freestanding shell in a revolving motion about the axis of said cylindrical shape and in a reciprocating motion along said axis to provide character selection;

said freestanding shell having radial resilience for permitting at least limited temporary deformation of said freestanding shell without compression or expansion of the rigid material thereof in response to a net linear radial force on said freestanding shell;

g. means for selectively applying a net linear radial force on said freestanding shell for providing a print impression in response to said net linear radial force to effect said limited temporary deformation;

h. mounting means at one end of said freestanding shell for mounting said freestanding shell to a carriage, and wherein said carriage includes said means for selectively applying a net linear radial force to said freestanding shell; and

. a plurality of perforations in said freestanding shell between said mounting means and said type impression characters for rendering said freestanding shell substantially uniformly resilient in the area wherein said type impression characters are located.

3. The combination as set forth in claim 1 and including:

a. mounting means at said one end ofsaid freestanding shell for mounting said freestanding shell to a carriage and wherein said carriage includes said means for selectively subjecting said freestanding shell to rotational and longitudinal forces; and

b. hammer means associated with said carriage and said freestanding shell to apply a net linear radial force to said freestanding shell for affecting at least a limited deformation of said freestanding shell to drive a selected type character towards a printing position. 

1. A multicharacter print element for a character-by-character printer comprising: a. a freestanding shell comprised of rigid material and having a cylindrical shape and inherent rotational and longitudinal rigidity and having substantially stable shell dimensions irrespective of the application of rotational and longitudinal forces; b. said freestanding shell also having radial resilience for permitting at least limited temporary deformation of said freestanding shell without compression or expansion of the rigid material thereof in response to a net linear radial force on said freestanding shell; c. a plurality of type impression characters disposed on the surface of said freestanding shell for providing a print impression in response to a net linear radial force on said freestanding shell to effect said limited temporary deformation; d. means for selectively subjecting said freestanding shell to rotational and longitudinal motions for positioning a selected one of said type impression characters at a predetermined printing position; and e. a plurality of perforations towards one end of said freestanding shell for rendering said freestanding shell substantially uniformly resilient in the area between said perforations and the other end of said freestanding shell.
 2. An alphanumeric print element comprising: a. a plurality of individual type impression characters; b. a freestanding shell comprised or rigid material having rotational and longitudinal rigidity; c. said freestanding shell and type impression characters assembled in cooperative relationship for maintaining each of said type impression characters in an individual fixed location on said freestanding shell; d. said freestanding shell having a cylindrical shape; e. means for selectively moving said freestanding shell in a revolving motion about the axis of said cylindrical shape and in a reciprocating motion along said axis to provide character selection; f. said freestanding shell having radial resilience for permitting at least limited temporary deformation of said freestanding shell without compression or expansion of the rigid material thereof in response to a net linear radial force on said freestanding shell; g. means for selectively applying a net linear radial force on said freestanding shell for providing a print impression in response to said net linear radial force to effect said limited temporary deformation; h. mounting means at one end of said freestanding shell for mounting said freestanding shell to a carriage, and wherein said carriage includes said means for selectively applying a net linear radial force to said freestanding shell; and i. a plurality of perforations in said freestanding shell between said mounting means and said type impression characters for rendering said freestanding shell substantially uniformly resilient in the area wherein said type impression characters are located.
 3. The combination as set forth in claim 1 and including: a. mounting means at said one end of said freestanding shell for mounting said freestanding shell to a carriage and wherein said carriage includes said means for selectively subjecting said freestanding shell to rotational and longitudinal forces; and b. hammer means associated with said carriage and said freestanding shell to apply a net linear radial force to said freestanding shell for affecting at least a limited deformation of said freestanding shell to drive a selected type character towards a printing position. 